A receiving apparatus for receiving a differential voltage signal requires a wide range of input common-mode voltages in order to cope with common-mode voltage offset or a low-voltage interface that is dependant on the conditions of a transmission apparatus and a transmission line. Such receiving apparatus is provided with a rail-to-rail circuit that has a signal conversion circuit for converting a common-mode voltage of an input differential signal into a predetermined voltage level and one or more differential amplifier circuits connected to a rear stage of the signal conversion circuit. For example, in an LVDS (Low-Voltage Differential Signaling) receiving apparatus that transmits/receives a digital signal by changing the direction of a current in a pair of differential transmission lines terminated by resistors, a signal conversion circuit converts an input common-mode voltage into a voltage that is higher than a value obtained by adding a predetermined offset voltage to a threshold value (Vthn) of an NMOS transistor, in order to operate a high-speed NMOS difference amplifier on a rear stage. Furthermore, it is required for the electronic devices that are operated with a low power-supply voltage to perform a so-called rail-to-rail operation to ensure a dynamic range in the circuit.
An input rail-to-rail signal conversion circuit described in Patent Document 1 has a differential amplifier circuit in which a pair of n-type transistors receives an input differential signal, and a source follower circuit in which a pair of p-type transistors receives an input differential signal and supplies a current to a pair of load resistors of the differential amplifier circuit. In this signal conversion circuit, the differential amplifier circuit is operated in a region where an input voltage level is higher than a first threshold voltage, and the source follower circuit is operated in a region where the input voltage level is lower than a second threshold voltage, whereby input rail-to-rail is realized complementarily. In a cooperative region where the input voltage level is at least the first threshold voltage but no more than the second threshold voltage, the differential amplifier circuit and the source follower circuit are operated together.
Another input rail-to-rail signal conversion circuit described in Patent Document 1 has a differential amplifier circuit in which a pair of p-type transistors receives an input differential signal, and a source follower circuit in which a pair of n-type transistors receives an input differential signal and supplies a current to a pair of load resistors of the differential amplifier circuit. In this signal conversion circuit, the differential amplifier circuit is operated in a region where an input voltage level is lower than a first threshold voltage, and the source follower amplifier circuit is operated in a region where the input voltage level is higher than a second threshold voltage, whereby the input rail-to-rail is realized complementarily. In a cooperative region where the input voltage level is at least the second threshold voltage but no more than the first threshold voltage, the differential amplifier circuit and the source follower circuit are operated together.
Patent Document 1 WO 2006/126436